Thread Whirl Parameters for Successful Thread Generation

Thread Whirling Parameters

Although Thread Whirling is quite simple there are a few parameters to understand:

1. Can Any Machine Be Used to Whirl? Not every machine can be used for whirling. The machine must be equipped with either a C-axis on the Main Spindle or Servo Type Main Spindle so can achieve programmed speeds of 10 or 20 RPM.

2. Threading Inserts - To achieve a unique desired thread shape, a special form insert which matches the desired thread form is required.

3. Depth of Cut - The max. DOC is dictated by the insert protrusion relative to the holder. This amount is approximately .100”

4. Maximum Dia. - The max. Diameter is dictated by the inscribed circle between the cutter tips. A clearance between the cutters and the work piece is required if a rapid retraction is desired.

In rare cases a larger diameter can be achieved up to the IC of the Cutter Ring. This requires the whirling cutters to feed on and then feed off at the same pitch rate similar to a die. Caution must be taken or the cutters, the cutter ring and the whirling spindle can be severely damaged.

5. Required Passes - With few exceptions, Whirling is generally accomplished in a single pass from stock diameter provided the maximum depth of cut is not exceeded.

6. Helix Angle – During the threading process proper cutter clearance is required to prevent the cutters from chipping out due to increase pressure on the edge. In the Whirling process, the whirling spindle with cutters is set at the thread Helix Angle relative to the part in order to provide the proper clearance on the side of the cutters as the whirling cutters move forward over the part. A cutter set at the wrong helix angle will also produce improper form and burrs.

7. Material That Can Be Whirled – Thread whirling can be accomplished on all metals, including some materials having a pre-hardened condition.

8. RPM - Whirling is more like a milling operation than a turning operation because of the interrupted cut. Therefore, the surface footage used to calculate the RPM is based more around milling.

9. Feed - The feed rate is dictated by the thread lead and is programmed in revolutions of the C-Axis, (main spindle) with a G32 or other programmed TPI G-code. As the speed of the C-Axis RPM increases or decreases the rate of travel of the Z-axis also increases or decreases automatically.

10. Chip load – The chip load is used to calculate the RPM of the C-Axis, (main spindle). This is based upon machining data recommendations for finish milling. Given that milling feeds are based upon heavy milling centers, the chip load is reduced to compensate for the lighter duty tool spindle conditions.

11. High Pressure Coolant – We require the use and of high pressure coolant accurately delivered to the front side of the cutting inserts. This provides the best chip evacuation to reduce the potential risk of fires and for optimizing tool life. If flammable materials are being machined the use of fire detection and fire extinguishing systems must be used